Change CONTRIBUTING title to 'Waterbear'

Changed the title from "Mobile Boilerplate" to "Waterbear", since... y'know, this is Waterbear.

---

Hey! I'm Eddie Antonio Santos, one of the UCOSP students. I'll be poking around in this repo before the sprint in January. Looking forward to making many more contributions to this project! Let me know if I'm adhering to stuff contribution wise. I understand there's [a lot](https://github.com/waterbearlang/waterbear/issues) [of things](https://github.com/waterbearlang/waterbear/blob/master/docs/how_you_can_help.md) to be worked on.